The present invention relates to an improved harmonic gear apparatus.
A typical example of a conventional harmonic gear apparatus will be explained referring to FIG. 1.
In FIG. 1, reference numeral 1 designates a rotary shaft rotated by a driving device (not shown); 2, a flexion generating member of a nearly oval configuration fixed to the rotary shaft 1 so as to be rotated with the rotary shaft 1; and 3, a cylindrical flexible spline made of a flexible material disposed around the outer periphery of the flexion generating member with the inner periphery thereof slidably and rotatably in contact with the outer periphery of the rotary shaft. The flexible spline 3 has a multiplicity of teeth 3a on the outer periphery thereof. Reference numeral 4 designates a circular spline attached to a fixing member (not shown) and having on an inner periphery a multiplicity of teeth 4a which can be engaged with the teeth 3a of the flexible spline 3 and whose number is larger than that of the teeth 3a.
The thus-constructed conventional harmonic gear apparatus operates as follows. When the rotary shaft 1 is rotated, the flexion generating member 2 rotates together with the rotary shaft 1 so that engaging portions of the teeth of the flexible spline 3 and the teeth of the circular spline 4 shift sequentially with the rotation of the flexion generating member 2. Thus, since the number N.sub.c of the teeth of the circular spline 4 is larger than the number N.sub.s of the teeth of the flexible spline 3 by a number (N.sub.c -N.sub.s), the flexible spline 3 rotates more slowly and in the opposite direction with respect to the flexion generating member 2. In this case, the gear reduction ratio n can be represented by n=(N.sub.c -N.sub.s)/N.sub.c.
In the conventional harmonic gear apparatus, in order to absorb the flexion of the flexible spline 3, the flexion generating member 2 is formed by a flexible member of a cup-like configuration whose circumferential portion protrudes axially, and the flexible spline 3 is provided on the open end of the flexible member. An output shaft is connected to a rear portion of the flexible member. Accordingly, since the flexible member of a cup-like configuration protrudes axially, the size of the harmonic gear apparatus in the axial direction is rather long.